On Monday, Phelps qualified for the finals in second place in his heat, one second ahead of le Clos. But the race will be remembered for Phelps' locked-in, almost furious game face. The hashtag #PhelpsFace was still trending on Twitter into Tuesday morning.

After the race, Phelps was asked what he was thinking about at the moment. The answer? Nothing — he was trying not to notice what was going on in front of him, the swimmer said.

"I was trying not to really even look at him," he said. "I was watching the heat in front of me and seeing how they were going."

Phelps said he's looking forward to get back into the water and race le Clos.

"He's tough," he said. "He finished on me last time really well and if I hit my turns the right way and swim the race I want to swim, that's all I can really do."

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But the meme stuck. Plenty of people found the determined face on the Olympics' most decorated athlete very relatable, while some wanted to know what music Phelps was listening to that got him feeling so pumped up.

The best part of it all might be that Phelps' newborn son, looking on in the stands with his trademark ear protection, put his own mean mug on for the cameras. Of course, baby Boomer Phelps is used to stealing the spotlight from his dad in Rio.